When a creator accepts a request, the request is temporarily listed as "being processed".
During this processing phase, pixiv will bill the requesting fan. The status of the request will change to "in progress" as soon as the billing goes through successfully.
Though it normally takes a few minutes for a request acceptance to be processed, if the fan's payment method requires reconfirmation by pixiv, or if an error occurs either in the pixiv servers or in the servers of the third-party payment service, this process may take up to a few days to complete.
All requests in the "being processed" phase cannot be canceled by the requesting fan or due to expiration of the response deadline.